Vacuum-tube repeater-circuits



H. S. READ.

VACUUM TUBE REPEATER CIRCUITS.

APPLICATION FILED APR. 12, 1919.

1,386,731., Patented Aug. 9, 19211..

' /n ve H far:

entree" stares rrsisr tries.

HARRY S. READ, OF EAST ORANGE, NEW JERSEY; ASSIGNOR TO WESTERN ELECTRICCOMPANY, INCORPORATED, 013 NEW YORK, N". 1., A CORPORATION OF NEW YORK,

Specification of Letters Patent.

HITS.

Application filed April 12, 1919. Serial No. 289,608.

To all whom it may concern:

Be it known that I, HARRY citizen of the United States, residing at EastOrange, in the county of Essex, State of New Jersey, have inventedcertain new and useful Improvements in Vacuum-Tube Repeater-Circuits, ofwhich the following is a full, clear, concise, and exact description.

This invention relates to vacuum tube r'epeaters and a method ofoperating the same, and more particularly to arrangements of suchrepeaters wherein the cathodes of a plurality of vacuum tubes are soconnected that heating current from a common source passes therethroughin series.

Vacuum tubes, when used in repeater circuits, are frequently found tooperate more satisfactorily when the control electrode is normallymaintained at a negative potential with respect to the cathode. Incircuits of the type above referredto, it has been proposed to obtainthe necessary steady potential difference between the control electrodeand the cathode of a vacuum tube, by connecting the control electrode ofone of the vacuum tubes to a point in the heating circuit such that thepotential of the control electrode is ne ative with respect to itscorresponding cathode by the drop in potential across the cathode ofanother tube. Such an arrangement is disclosed andclaimed in the patentapplication of E. O. Scriven, Serial No. 242,183, filed June 27, 1918.

In certain circuits of this type it has been found that the negativepotential of the control electrode, if derived from the total dropacross another tube, is rendered too great for the proper operation ofthe corresponding tube.

It is an object of this invention to provide a simple, easily controlledmeans for applying only a portion of the potential drop across a cathodeto the control electrode of another tube.

This is accomplished in the preferred form of the invention byconnecting a resistance across the terminals of a cathode and tappingofl from a point on this resist ance through a connection to the controlelectrode of another tube.

In circuits employing a plurality of vacuum tubes of different types,some of the tubes may require more cathode heating current than others.To prevent overheating S. READ, a

of such cathodes when all the cathodes are connected in series to asource of heating current, this invention provide a method and means forby-passing a portion of the current about each of the cathodes likely tobe overheated. This insures sutlicient hurrent in the other cathodeswhen the potential of the source is limited. :In certain instances thisby-path serves the threefold purpose of (1) preventing overheating inthe cathode that can use less current, (2) causing suificient current inthe filament that can use more current, and (3) providing a means forsupplying to the control electrode of another tube a potentialcorresponding to that of a point intermediate the ends of the cathodewhich is shunted by the resistance.

The invention will be more fully understood from the following detaileddescription and claims taken in connection with the accompanying drawingwhich shows diagrammatically a detector-amplifier circuit embodying theinvention.

Referring to the drawing by reference numerals, the vacuum tube 10 isemployed in a detector unit having its input circuit connected at theterminals 11 and 12 in any desired or usual manner to a receivingantenna or other circuit adapted to have signal impulses producedtherein. The input circuit contains a series condenser 13 and a shuntcondenser 14: and is grounded at 15.

The output circuit of tube 10 is connected to the first tube of athree-stage amplifier comprising the vacuum tubes 16, 17 and 18, allfour of the tubes 10, 16, 1? and 18 being arranged in tandem. Thefilamentary cathodes 19, 20, 21 and 22 of tubes 10, 16, 17 and 18 .arein series with each other and with a source of heating current shown inthe drawings as a battery 10, having its negative pole directed towardthe adjustable resistance 23.

While in .the drawings all of the tubes are shown schematically as beingalike, in the actual circuit which is represented herein,

tubes 10 and 18 were of a type operating more satisfactorily with a.lower filament temperature than tubes 16 and 17, and to prevent theoverheating of cathodes 19 and 22, shunt resistances 24 and 25 wereprovided to carry a portion of the current. Values of 25 ohms and 20ohms, respectively,

Patented Aug. 2, 1921.

were found to be suitable for these resistances.

Space current is supplied to allof the tubes from a source shown in thedrawings as'a battery 41, the negative pole of which is connected to thecathode heating circuit and the positive pole is connected to the plateelectrodes or anodes 26 in multiple through the resistances 27. Aninductance 28 is also placed in the path to the anode of the detectortube 10, and a condenser 29 is bridged across the output circuit of thistube. The anode of each tube is connected to the grid or controlelectrode 30 of the succeeding tube through a condenser 31.

The tube 16 is found to operate more satisfactorily, if its grid 80 isnormally maintained negative with respect to cathode 20 by a potentialdifference less than the drop in potential of the heating currentthrough the preceding cathode 19. This negative potential is pbtained byconnecting the grid through resistance 32 to a suitable tap on theresistance 24. In the circuit set up as above referred to, the portion24 of this resistance, was 20 ohms and the portion 24 was 5 ohms. Asimilar connection is made to the grid of tube 17 from a resistance 35bridged across the cathode 20. This resistance had a value of 125 ohmsso as to bypass only a negligible amount of heating current, andsatisfactory operation was obtained when the grid connection divided itinto two parts 35 of 100 ohms and 85 of 25 ohms.

A means for controlling the ratio of amplification of the set isprovided in the resistance 36 which is arranged .as a potentiometer withto the grid of tube 17. A

The negative grid potential for the tube 18 in this circuit is requiredto be greater than for the preceding tubes, and is obtained by aconnection through the resistance 37 to a point adjacent the negativeend of the filament 21', thereby obtaining the total drop in potentialacross this filament.

The output from the tube 18 passes through a suitable receiving device38, shown as a telephone receiver, and a path for alternating currentsis provided by the condenser 39. r

While a more uniform amplification throughout a wide range of signalfrequencies can be obtained by using non-inductive resistances 27 32, 36and 37, satisfactory operation canalso be had if these resistances areinductive. For example, in the output circuit of the detector tube 10,the inductance 28- is inserted in series with the resistance 27 in orderto provide the desired impedance to alternating currents.

While the invention has been shown embodied in a specific circuit, it isto be under-- stood that it is of general application in cira series oftaps for connectioncuits employing a plurality of vacuum tubes and is tobe limited only by the scope of the following claims.

What is claimed is: 1. In a multi-stage repeater, a plurality ofelectrode of another of said tubes substantially at the same potentialas that of a point intermediate the ends of said first mentionedcathode.

3. In combination, a plurality of vacuum tubes arranged in'tandem, saidtubes having filamentary cathodes so connected that heating current-flows serially through said cathodes, a resistance bridged across oneof said cathodes, and a connection from a point on said resistance tothe control electrode of another of said tubes.

4:. In amulti-stage repeater, a'p'lurality of vacuum tubes each having acathode, an anode and a' control electrode, said cathodes being. soconnected that heating current flows serially therethrough, a resistancebridged across one of said cathodes, and a connection from a point onsaid resistance to the control electrode corresponding to a cathodewhich is more positive than said first-mentioned cathode.

5. In a multi-stage repeater, a plurality of vacuum tubes each having acathode, an anode and a control electrode, and means comprising aresistance bridged across the cathode of one of said tubes formaintaining the control electrode of another of said tubes atsubstantially the same otential as that of a point intermediate t e endsof said cathode.

6. A vacuum tube translating device comprising a cathode, an anode and acontrol electrode, a source of heating current in circuit with saidcathode, a low resistance'serially connected between said cathode andsaid source, a high resistance in shunt to a portion of said heatingcurrent circuit including said low resistance, and a connectionvacuumtubes 'each having a cathode, an

cuit with said cathode, a low resistance serially connected between saidcathode and the negative terminal of said source, a high resistance, aconnection from said hi h resistance to a portion of said heatingcircuit,

a second connection from said high resistance to another portion of saidheating circuit, said high resistance being in shunt to a portion ofsaid heating current circuit including said low resistance, and a thirdconnection from said high resistance and leading to said controlelectrode.

8. In combination, a plurality. of vacuum tubes each having a cathode ananode and a control electrode, said cathodes being so connected thatheating current passes serially therethrough, one of said tubes being ofa type which requires less heating current 20 than another of saidtubes, a resistance bridged about the cathode of said first mentionedtube, and a connection from a oint on said resistance to the controlelectrode of another of said tubes.

9. In combination, a plurality of vacuum tubes each having a cathode, ananode and a control electrode, said cathodes bein so connected thatheating current flows serlally therethrough, a resistance in shunt to aportion of the heating current circuit contain ing one of said cathodes,and means comprising a connection from an intermediate point on saidresistance to the control electrode of another of said tubes fordetermining the potential difi'erence between said last mentionedcontrol electrode and its cathode.

In witness whereof I hereunto subscribe my name this 10th day of April,A. D, 1919.

